Scotch marine style boiler with removable tube bundle

ABSTRACT

A boiler includes a cylindrical shell sealed at both ends. A working liquid, typically water, circulates inside the shell. A tube bundle is seated inside the shell. Hot combustion gases circulate inside the tube bundle, heating the water circulating inside the shell. The tube bundle includes a relatively large inlet tube that runs straight to a distal end, where hot combustion gases are turned 180° by a concave inner surface on the tube bundle header, which is not a part of the shell, and are returned by a plurality of smaller diameter return tubes and then to an exhaust stack. The tube bundle includes a front tube sheet and a distal end tube sheet that the tubes are welded to, but these tube sheets are not part of the shell. The entire tube bundle floats inside the shell without being fastened to the shell except at the front of the tube bundle, where a baffle is secured to the front opening of the shell. This allows the tube bundle to be removed from the shell as a single unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT.

[0002] Not applicable.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention is related to an apparatus for providing a heated working liquid. More particularly, the present invention is directed to a Scotch Marine style boiler having a removable tube bundle, which has a single un-insulated metal inlet tube for receiving hot combustion gases and a plurality of return tubes that are parallel to the inlet tube and convey hot combustion gases in opposite directions, with the gases being turned 180° by a concave tube-bundle dome on the distal end of the tube bundle, which is not a part of the shell.

[0005] 2. Description of the Related Art Including Information Disclosed Under 37 C.F.R. 1.97 and 1.98.

[0006] Scotch marine style boilers having a sealed shell with a plurality of heat exchange tubes sealed inside the shell are well known. Typically all the joints are welded. Such provides access to the interior of the shell and limited access to the tubes that comprise the tube bundle.

[0007] Since the heat exchange tubes are welded into the ends of the shell, these boilers are subject to thermal shock, which can cause leaks in weld joints, from split tubes and the like unless the entire boiler is heated gradually to its equilibrium operating temperate and cooled gradually when it is removed from service. The possibility of damage from thermal shock requires careful and skillful operation of the boiler; decreases the convenience of utilizing the boiler for power, and increases fuel consumption. It also greatly increases the time required to obtain useful power from the boiler after firing begins.

[0008] Repairing damaged tubes requires that a worker enter the man way and squeeze into the shell and cut out the defective tubes with a cutting torch. Thorough inspection of the tube bundle or the interior of the shell is not possible and any work inside the boiler is very labor intensive, expensive and potentially dangerous. This process is so uncertain and laborious that these types of boilers are often scraped when the tubes require significant maintenance, resulting in significant waste of resources.

[0009] Therefore, there is a need for a boiler having a removable tube bundle; that is not subject to thermal shock; and that would consequently be easier to work on than prior art boilers.

BRIEF SUMMARY OF THE INVENTION

[0010] Accordingly, it is a primary object of the present invention to provide a boiler having a removable tube bundle.

[0011] It is another object of the present invention to provide a boiler that is not subject to thermal shock.

[0012] It is another object of the present invention to provide a boiler that is easier to work on than prior art boilers.

[0013] These and other objects of the invention are achieved by providing a shell, basically cylindrical in shape, having a sealed distal end and a forward end that is sealed by a flange member connected to the tube bundle. The tube bundle is self-contained, that is, its integrity and functionality is independent of the shell. The tube bundle is inserted into the shell along sliding rails secured to the bottom of the tube bundle, which slide along rails that are secured to the lower interior surface of the shell.

[0014] Because the tube bundle is a self-contained unit that is fastened to the shell only at the front header and otherwise rests on and floats on rails inside the shell, the boiler is not subject to thermal shock and so does not need to be coddled when heating and cooling the boiler.

[0015] When the tube bundle is removed from the shell, the tube bundle is fully accessible to workers, who may carefully inspect it, perform a full visual inspection and work on it conveniently, while at the same time, the interior of the shell is readily accessible for inspection and repair. Further, it is easily possible to replace the entire tube bundle. In the existing Scotch marine boiler, replacement of the tube bundle is not feasible. The ability to readily replace the tube bundle in the present invention dramatically reduces repair and refurbishment costs associated with maintain boilers and can greatly extend the life of the entire boiler.

[0016] For example, in an 745 kilowatt (100 HP) Scotch marine boiler, re-tubing the boiler would take 32 man hours to accomplish, with not more than two men able to work on the project at the same time. Utilizing the present invention, about nine man hours of labor would be required to re-tube the boiler. Further, more than two men can work on re-tubing the boiler at the same time.

[0017] The present invention is a modification of a complete boiler system, including the burner element and controls, which is fully described in my U.S. patent application Ser. No. 09/391,790, filed Sep. 8, 1999, now issued as U.S. Pat. No. ______ B1, which is hereby incorporated herein by reference.

[0018] Other objects and advantages of the present invention will become apparent from the following description taken in connection with the accompanying drawings, wherein is set forth by way of illustration and example, the preferred embodiment of the present invention and the best mode currently known to the inventor for carrying out his invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0019]FIG. 1 is right-hand front perspective view of a boiler according to the present invention.

[0020]FIG. 2 is a right-hand front perspective view of the boiler of FIG. 1 with the tube bundle removed and in position for insertion into the shell.

[0021]FIG. 3 is the right-hand front perspective view of the boiler as in FIG. 3 illustrating the hidden parts of the boiler.

[0022]FIG. 4 is a side elevation of the boiler of FIG. 1 with the tube bundle removed and in position for insertion into the shell.

[0023]FIG. 5 is a schematic front elevation of the shell of the boiler of FIG. 1, illustrating an end view of the vertically oriented rails secured to the interior of the shell and the horizontal rails that are secured to the bottom of the tube bundle that slide along the vertically oriented rails during insertion and removal of the tube bundle from the shell.

[0024]FIG. 6 is a side elevation of the vertically oriented rails that are welded to the lower inside surface of the shell.

[0025]FIG. 7 is a cross sectional view taken along lines 8-8 of FIG. 3.

[0026]FIG. 8 is a perspective view of the header on the distal end of the tube bundle showing the concave interior surface of the header, or tube bundle dome.

DETAILED DESCRIPTION OF THE INVENTION

[0027] As required by the Patent Statutes and the case law, the preferred embodiment of the present invention and the best mode currently known to the inventor for carrying out the invention are disclosed in detail herein. The embodiments disclosed herein, however, are merely illustrative of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely to provide the proper basis for the claims and as a representative basis for teaching one skilled in the art to which the invention pertains to make and use the apparatus and process disclosed herein as embodied in any appropriately specific and detailed structure.

[0028] Referring to FIG. 1, the Scotch marine style boiler, or boiler 10, includes a shell 12 having a cylindrical main body 14 with a distal end dome 16 permanently sealed onto the cylindrical main body 14, which seals the distal end of the cylindrical main body 14. The structure for sealing the distal end of the shell 12 is a matter of design choice. In low pressure applications, the welded dome 16 having a perpendicular collar 17 that is welded to the shell cylindrical body 13 is adequate. In high-pressure applications, it is preferable to construct a flange on the distal end of the shell 12 and bolt a flat plate to the flange. A man way 18 consisting of a circular opening 20 in the top of the cylindrical main body 14 adjacent to the distal end dome 16 with an upstanding collar member 22 fastened to the cylindrical main body 14 about the perimeter of the circular opening 20, which is sealed by a removable man way cover 24 in a well-known manner, which is moved along the arrow 2 during installation. Access ports 26 are provided for the insertion of various sensors essential to the safe operation of the boiler 10. These sensors are well-known in the art.

[0029] Still referring to FIG. 1, the boiler is secured to a mounting cradle 30 to keep the cylindrical boiler from rolling around. The base of the mounting cradle 30 is wide enough to provide a stable base for the boiler 10 and may itself be bolted or otherwise fastened to the floor, deck or the like and is also useful in transporting the boiler 10.

[0030] Still referring to FIG. 1, the front cover 32 of the boiler 10 is circular in plan view and includes a plurality of holes 34 adjacent to its circumference, which align with matching holes 36 about the circumference of a connecting circular flange 38 connected onto the front end of the cylindrical body 14 of the boiler 10. The front cover 32 is fastened to the circular connecting flange 38, which is fastened to a front edge of the shell 12, by the nuts and bolts 40. A high temperature gasket 42 is interposed between the circular flange 38 and front cover 32. A high-temperature tube bundle gasket 41 fits onto the front end of the tube bundle 48 and includes apertures for the inlet tube 64 and a single aperture for the return tubes 74, each having a front end 75. A reinforcing and locating plate 44 has a substantially oval shape with an upper opening 46 for admitting combustion gases into the tube bundle 48 (See especially FIG. 3) and an exhaust opening 50 in the lower portion of the locating plate 44 for allowing the exhaust gases to exit the tube bundle 48. The locating plate 44 is connected to the front cover by nuts and bolts 52 inserted through the plurality of apertures 54 adjacent to the perimeter of the locating plate 44 and the aligned apertures 56 in the front cover 32. An upper opening 55 and a lower opening 57 in the front cover 32 align with the inlet opening 46 and the exhaust opening 50 in the locating plate 44. Thus the front cover 32 serves to seal the tube bundle 48 into the shell 12 and to seal the front end of the shell 12 itself.

[0031] A burner (not shown) is connected to the upper opening 46 to direct hot combustion gases into the tube bundle 48. If the burner is capable of projecting a long thin flame encircled by a layer of insulating air, which is the preferred type of burner, then the flame can be projected directly into the tube bundle 48, all of which is made from typical tube bundle steel without any insulation either inside or outside the tube material. Alternatively, an external conventional fire tube (not shown) having, for example, a lining of refractory brick, may be connected to the upper opening 46, in which case a conventional burner on the distal end of the fire tube provides the hot combustion gases to heat the tube bundle 48. When a conventional burner is used, the fire tube must provide combustion gases to the tube bundle 48 that are cool enough that they do not melt the tubes.

[0032] The boiler 10 may be used to produce either steam or hot water from feed water that is circulated through the shell 12 by external an external pump (not shown). When used as a water heater, the feed water enters the shell 12 through the water inlet 58 (FIG. 4) located in the bottom of the shell 12 inward from the dome 16 by about ⅛th the length of the shell 12 and the hot water exits from the boiler 10 through the hot water outlet port 60 on the top of the shell 12 adjacent to the burner inlet end of the shell 12. When the boiler is used to produce steam, the steam exits the boiler 10 from the same outlet port 60 as hot water does, while the feed water is introduced to the boiler 10 through the boiler feed water inlet port 62 located in the middle of the length of the shell 12 about 5 cm (2 inches) below the lowest possible firing level of water in the shell 12. The boiler 10 may be scaled to provide power throughout a wide range and the physical size of the boiler and accompanying controls, inlets, outlets and the like are determined by the load requirements of a particular application.

[0033] Referring to FIGS. 2, 3, and 4, the tube bundle 48 includes a relatively large diameter straight inlet tube 64 having an inlet end 66 for the admission of hot combustion gases from a burner and an outlet end 68 that is welded to the distal end tube sheet 70, which is connected to a header, or tube bundle dome, 72 having an internal surface 71 that is concave, as best shown in FIG. 8. Twenty-eight straight return tubes 74 of smaller diameter than the inlet tube 64, with the exact number a matter of design choice, each includes a distal end 76 that is welded to the distal end tube sheet 70. The distal end tube sheet includes aligned apertures for permitting the gases to pass through the tubes and the distal end tube sheet 70 in the conventional manner. The return tubes 74 are gathered into a bundle that collectively exhausts the spent combustion gases through the lower opening 50 in the locator plate 44, through the front ends 75 of the return tubes 74, which exhaust the spent combustion gases. The exhaust gas is then passed through an exhaust stack (not shown) that is connected to the lower opening (exhaust opening) 50 in the locating plate 44. The hot combustion gases are introduced into the inlet tube 64 and flow through the inlet tube in the direction of the arrow 78, are turned around 180° by the internal surface of the header, or tube bundle dome, 72 and then flow through the return tubes 74 along the direction of the arrow 80. The inlet end 66 of the inlet tube 64 and the front ends 75 of the return tubes 74 are welded to the front tube sheet 82, which has aligned apertures for allowing the passage of gases from the tubes through it in the conventional manner. The inlet end 66 of the inlet tube 64 and the front ends 75 of the return tubes 74 lie in the same plane, oftentimes facilitating installation of the boiler 10.

[0034] The specific diameters of the tubes 64, 74 and the number of return tubes 74 is calculated in accordance with the total volume of combustion gases that have to be extracted from the from the return tubes, which are equipped with turbulators in the conventional manner to maintain a desired velocity of gas throughout all the tubes 64, 74.

[0035] Referring to FIGS. 2, 3, 4, three spaced apart baffles 84 include apertures 86 that the inlet tube 64 and return tubes 74 pass through. The tubes 64, 74 are not fastened to the baffles 84, but are free to float within the apertures 86. The apertures 86 help to support the tubes 64, 74 and to maintain the proper spacing of these tubes, but the principal purpose of the baffles is to help direct the flow of water or steam throughout the shell 12 to improve heat transfer. The baffles 84 have a profile in the broad dimension that is 63% of the surface area of a cross section of the shell 12. The principal purpose of the baffles 84 is to slow the velocity of the working fluid that flows through the shell 12 and to maximize the time of contact between the water or steam and the tubes 64, 74 to increase the efficiency of the heat transfer from the tubes 64, 74 to the working fluid. The greater the desired flow rate of the working fluid through the shell 12, the greater the number of desired baffles is.

[0036] Welded to the lower surfaces of the baffles 84 are a pair of skid rails 88, which are parallel spaced apart metal bar stock members oriented with the width of the rails being horizontally oriented (See especially FIG. 5). These skid rails 88 allow the tube bundle 48 to be slid into the shell 12 by riding along the skid members 90, that are welded into the shell 12 along the lower portion of the shell 12 at regular intervals of about 3 cm (See especially FIG. 5), and that consist of metal bar stock members that are oriented so that width is vertical and the skid rails 88 ride on the edge of the bar stock. That is, the skid rails 88 can slide along the top of the aligned skid members 90, with the skid rails 88 being welded to the baffles 84 and the skid members 90 being welded to the lower surface of the inside of the shell 12. This system allows the tube bundle 48 to be slid into the shell 12 in the direction of the arrow 92 and to be removed by reversing this direction. Referring in particular to FIG. 6, each skid member 90 has a lower edge 91 with drainage notches 93 formed in it at regular intervals throughout the length of the skid members 90, which may be semi-circular as shown or another shape. There drainage notches prevent stagnant areas near the skid members 90, thereby preventing the accumulation of sludge along the skid members 90. FIG. 7 illustrates an end elevation of the tube bundle 48.

[0037] A front tube bundle flange 94 is circular and includes an upper circular opening 96 that the inlet tube 64 penetrates and a large roughly half-moon opening 98 that holds the outlet end of the return tubes 74. The tube bundle flange 94 seals the tube bundle 48 against the mounting flange collar 38 on the front edge of the cylindrical portion of the shell 12, with the high-temperature gasket 42 being seated between these two surfaces.

[0038] Utilizing the preferred burner, the boiler 10 achieves a fuel to product efficiency of 85%+ and an NOX emission level of 1 on the conventional NOX scale of 1-800. Many boilers are capable of NOX emissions of only 350 and government regulations will soon require levels of 10 or fewer, which the boiler 10 can easily meet.

[0039] While the present invention has been described in accordance with the preferred embodiments thereof, the description is for illustration only and should not be construed as limiting the scope of the invention. Various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention as defined by the following claims. 

I claim:
 1. A boiler comprising: a. a shell; b. a tube bundle exchanger seated inside said shell, said tube bundle comprising one inlet tube adapted to direct combustion gases in one direction and at least one return tube in fluid communication with said inlet tube adapted to direct combustion gases in the opposite direction.
 2. A boiler in accordance with claim 1 further comprising means for redirecting the flow of hot gases from said inlet tube 180° to pass through said return tube.
 3. A boiler in accordance with claim 2 where in said gas redirecting means further comprises a tube-bundle dome having a concave interior surface, with said dome being fixed onto said distal end of said tube bundle, wherein said tube bundle dome is not part of said shell.
 4. A boiler in accordance with claim 1 wherein said inlet tube and said at least one return tube are parallel to each other.
 5. A boiler in accordance with claim 3, wherein said tube bundle further comprises a distal end tube sheet that said tubes are fastened to and a front end tube sheet to which said inlet tube and said at least one return tube are fastened.
 6. A boiler in accordance with claim 4 wherein said tube bundle comprises an integrated unit that is removable from shell.
 7. A boiler in accordance with claim 5 further comprising means for installing or removing said tube bundle in said shell.
 8. A boiler in accordance with claim 6 wherein said installation and removal means further comprises a pair of skid rails mounted on said heat exchanger and a pair of skid members mounted on a lower portion of an inside lower surface of said shell, whereby said tube bundle can be slid into or out of said shell.
 9. A boiler in accordance with claim 7 further comprising means for sealing said tube bundle inside said shell.
 10. A boiler in accordance with claim 6 wherein said tube bundle further comprises a plurality of spaced baffles, each said baffle having a plurality of apertures with said inlet tube and said at least one return tube passing through one said aperture of each baffle, with each said tube free to float within said apertures.
 11. A boiler comprising: a. a shell; b. a tube bundle exchanger seated inside said shell, said tube bundle comprising one inlet tube adapted to direct combustion gases in one direction and a plurality of return tubes in fluid communication with said inlet tube adapted to direct combustion gases in the opposite direction; and c. means for inserting and removing said tube bundle from said shell.
 12. A boiler in accordance with claim 11 wherein inserting and removing means further comprises a pair of spaced parallel skid rails fixed to a lower surface of said baffle and a pair of spaced parallel skid members fixed to a lower inner surface of said shell and said skid rails and said skid members are aligned to allow said tube bundle to slide along said skid members into and out of said shell.
 13. A boiler in accordance with claim 11 wherein said inlet tube and said outlet tubes further comprise un-insulated metal tubes.
 14. A boiler in accordance with claim 11 wherein said tube bundle further comprises a tube bundle dome on distal ends of said inlet tube and said return tubes, wherein said tube bundle dome is not a part of said shell.
 15. A boiler in accordance with claim 14 wherein said tube bundle dome further comprises an inner concave surface adapted to turn hot combustion gases 180° back on itself from the direction of flow through said inlet tube for flow for said return tubes.
 16. A boiler in accordance with claim 11 further comprising means for sealing said tube bundle; means for sealing said tube bundle inside said shell and means for sealing a distal end of said shell.
 17. A boiler comprising: a. a shell; b. a tube bundle exchanger seated inside said shell, said tube bundle comprising one inlet tube adapted to direct combustion gases in one direction and a plurality of return tubes in fluid communication with said inlet tube adapted to direct combustion gases in the opposite direction, and a tube bundle dome having a concave inner surface, said tube bundle dome fastened to said inlet tube and to said return tubes, whereby said concave inner surface turns the hot combustion gases 180° from their direction of flow through said inlet tube to flow toward in the opposite direction. c. a plurality of parallel baffles spaced along the length of said inlet tube and said return tubes; and d. means for inserting and removing said tube bundle from said shell.
 18. A boiler in accordance with claim 17 where in said baffles further comprise a plurality of apertures with said inlet tube and said at least one return tube passing through one said aperture of each baffle, with each said tube free to float within said apertures.
 19. A boiler in accordance with claim 17 further comprising means for inserting and removing said tube bundle from said shell.
 20. A boiler in accordance with claim 17 further comprising means for sealing said tube bundle; means for sealing said tube bundle inside said shell and means for sealing a distal end of said shell. 